dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Sun, Oct 18, 2009 at 01:15:46PM -0400, mspieg wrote:
>
> On Oct 16, 2009, at 6:04 PM, Anders Logg wrote:
>
>
>     On Fri, Oct 16, 2009 at 03:34:06PM -0400, mspieg wrote:
>
>         Hi All,
>           I'm trying to update a working 0.9.3 code to  0.9.4, and I need to
>         understand
>         the new interfaces for Function::eval a bit better.
>
>         I had things working fine with the old interface
>
>         Function::eval (double *values, const double *x, const ufc::cell &
>         ufc_cell,
>         uint cell_index)
>
>         and am trying to understand how to efficiently use
>
>         Function::eval (double *values, const double *x, const Cell &
>         dolfin_cell, const
>         ufc::cell &ufc_cell)
>
>         (My codes need to do a large number of evals at arbitrary points and
>         cells
>         efficiently)
>
>         among other things, is there an easy way to update the index of a cell,
>         without
>         constructing a new Cell every time? (or shouldn't I be worrying about
>         this).
>
>
>     Constructing a cell should not cost that much. It just stores the
>     index, the dimension and a reference to the mesh.
>
>     If you are using iterators over a mesh, then you already have the cell
>     by dereferencing the pointer. The typical usage would be
>
>     UFCCell ufc_cell(mesh);
>     for (CellIterator cell(mesh); !mesh.end(); ++cell)
>     {
>       ufc_cell.update(*cell);
>
>       f.eval(values, x, *cell, ufc_cell);
>     }
>
>     But perhaps you don't use iterators?
>
>
> Thanks Anders,
>   I haven't been using iterators because I've been overloading eval(double*
> values, Data& data) and getting the cells passed through data during assembly
>
> the issue is that I'm not necessarily evaluating at the position and cell in
> data, but at another point and cell derived from the current location and cell
> (it's basically a particle tracking problem).
>
> Ideally, given data I would set another Data structure (data_prime) with the
> new point, cell and ufc_cell, then call eval as needed.  As long as the cost to
> construct a cell is small, it will probably be easy enough to do with the
> current code (the problem is I need to do this at every quadrature point, and I
> found previously that construction of UFCCell at every point was exceptionally
> expensive).
>
> Anyway, I'll play around a bit more and if I have specific issues or design
> questions, I'll let you know.
>
> cheers
> marc

ok. Sounds good. Let us know if you discover (by profiling or similar)
that the cost is large for creating a Cell. If so we may consider some
fixes for it.

--
Anders


>
>
>
>
>
>
>         Anyway, I need to play with things a bit more, but looking at the
>         source code
>         for eval,  I was also wondering
>          if lines 320 and 321 are required as line 322 doesn't seem to require
>         cell.
>
>          typo? bug? or general ignorance on my part (probably the latter).
>
>
>     Yes, lines 320-321 should be removed. Thanks for noticing. I've fixed
>     this now.
>
>
>
>
>         cheers
>         marc
>
>         void Function::eval(double* values, const Data& data) const
>
>         00311 {
>         00312   assert(values);
>         00313   assert(_function_space);
>         00314
>         00315   // Check if UFC cell if available and cell matches
>         00316   if (data._dolfin_cell && _function_space->has_cell
>         (*data._dolfin_cell))
>         00317   {
>         00318     // Efficient evaluation on given cell
>         00319     assert(data._ufc_cell);
>         00320     const uint cell_index = data._ufc_cell->entity_indices
>         [data._ufc_cell->topological_dimension][0];
>         00321     Cell cell(_function_space->mesh(), cell_index);
>         00322     eval(values, data.x, *data._dolfin_cell, *data._ufc_cell);
>         00323   }
>         00324   else
>         00325   {
>         00326     // Redirect to point-based evaluation
>         00327     eval(values, data.x);
>         00328   }
>         00329 }
>
>         ----------------------------------------------------
>         Marc Spiegelman
>         Lamont-Doherty Earth Observatory
>         Dept. of Applied Physics/Applied Math
>         Columbia University
>         http://www.ldeo.columbia.edu/~mspieg
>         tel: 845 704 2323 (SkypeIn)
>         ----------------------------------------------------
>
>
>
>
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>
> ----------------------------------------------------
> Marc Spiegelman
> Lamont-Doherty Earth Observatory
> Dept. of Applied Physics/Applied Math
> Columbia University
> http://www.ldeo.columbia.edu/~mspieg
> tel: 845 704 2323 (SkypeIn)
> ----------------------------------------------------
>
>

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